If Williams can build on her 6-4, 6-0 win on a sultry Monday night on Arthur Ashe and capitalise on the earlier shock defeat of Simona Halep in her corner of the draw, she has every chance of doubling her season's earnings of US$1.9 million (S$2.6 million).
Bumped up to 17th seed from her world ranking of 26 because of her pedigree and record, Williams looked relaxed, fitter than recently and ready to contend.
Her serve was grooved and she hit off the ground with her customary menace. She even threw in a rare drop shot before serving out the match with her sixth ace.
Her movement was better than when she reached the Wimbledon final this year, assured rather than electric.
She said: "It's just a good feeling to be back out here. The first set was tight, not the easiest. Once I got settled, I started to doing what I tried to do in practice.
"I think I'm getting there. I've been training so hard. This momma was a little emotional today."
Today, she will play the world No. 101 Carina Witthoeft, who beat American Carolina Dolehide 6-3, 7-6 (8-6) on Monday.
If she prevails over the 23-year-old German, she could face her older sister, Venus, in the third round on Friday, when the weather is expected to have cooled a little. Venus survived a stern test in the heat of the day before beating 2004 champion Svetlana Kuznetsova in three sets.
A year ago, Williams, the oldest of seven mothers in the draw at 36, was only days away from giving birth to Alexis Olympia by emergency C-section, when she survived a pulmonary embolism. There was no guarantee she would even play again, given the serial clotting she endured.
"It's just a bonus to step out here tonight," she said before going on court.
As Chris Evert observed: "She might be the greatest player of all time, but she's still human. She's fallen madly in love with her child, and wants to cuddle her and nurture her, and then she's got to go out and handle the pressure on the court."
Meanwhile, world No. 1 Halep said there is no mystery to her shock 6-2, 6-4 loss to big-hitting Estonian Kaia Kanepi on Monday.
The emotional Romanian, who went out in the first round last year to Maria Sharapova, became the first top-seeded woman to lose in the first round of the US Open in 50 years of professional-era tennis.
"I just lost. The balance was not there. I couldn't feel myself strong on the court to win this match," said the 26-year-old.
"It's not a drama. It's just a bad day for me. But also, she deserved to win because she was playing better than me today. So it's nothing about pressure. It was just a day."